1. Field of the Invention
The present invention relates to a heat treatment method and a heat treatment apparatus for heating a substrate such as a semiconductor wafer with a high dielectric constant film formed thereon by irradiating the substrate with light, thereby promoting the crystallization of the high dielectric constant film.
2. Description of the Background Art
Hitherto, silicon dioxide (SiO2) has been typically used as the material of a gate insulator film for a field-effect transistor (FET). However, as gate insulator films are made thinner with the decreasing size of devices, the increase in leakage current has become a problem. To solve the problem, a metal gate electrode such that metal is used as the material of a gate electrode has been developed while a material (a high dielectric constant material or a high-k material) having a relative dielectric constant higher than that of silicon dioxide is used as the material of a gate insulator film, as disclosed in U.S. Pat. No. 7,989,283.
However, a problem to be described below arises during the heat treatment of a semiconductor wafer on which a high dielectric constant film (a high-k film) is formed as the gate insulator film. The high dielectric constant film is formed by depositing a high dielectric constant material, using a MOCVD (metal organic chemical vapor deposition) technique and the like. In recent years, attention has also been given to an ALD (atomic layer deposition) technique in which atomic layers are deposited one by one. In either technique, the high dielectric constant film just deposited without any post processing is low in crystallinity. It is hence necessary to anneal the high dielectric constant film at 1000° C. or higher, thereby promoting the crystallization of the high dielectric constant film.
The heating of the high dielectric constant film to 1000° C. or higher over a prolonged period of time of several seconds or more, however, gives rise to a problem such that the movement of oxygen grows a film of silicon dioxide present between the high dielectric constant film and silicon serving as a base material to increase the thickness of the film of silicon dioxide, thereby lowering device characteristics.
Additionally, interfaces between the deposited high dielectric constant film and the underlying silicon dioxide film and between the deposited high dielectric constant film and a metal gate electrode to be formed thereover are inevitably lower in quality as compared with an interface between silicon and silicon dioxide. It is hence required to improve the interface characteristics of the high dielectric constant film when the high dielectric constant film is used as the gate insulator film.